Evaluation of the effect of aging on intracellular free potassium, magnesium and calcium: relation to hypertension and diabetes

ABSTRACT

Elevated cytosolic free calcium [Cai], potassium [Ki], magnesium [Mgi] and reciprocally disturbed, extracellular ionized calcium, potassium and magnesium levels are observed in both hypertension and non-insulin-dependent diabetes mellitus [NIDDM]. Because the changes of vascular function and insulin sensitivity in these conditions resemble the changes associated with [normal] ageing, we wondered to what extent similar alterations in calcium, potassium and magnesium metabolism occur with aging per se in the absence of hypertension or diabetes. We therefore measured platelet Cai, Ki and Mgi levels by spectrofluorometry and serum Ca, K, Mg-ion levels in normotensive, nondiabetic, healthy, elderly subjects, mean age 68.5 +/- 3.5 years old [n=11]; in healthy, normal, young adults, 43.2 +/- 3.4 years old [n=13]; in 11 young adult hypertensives, 41.3 +/- 3.7 years old; and in 9 normotensive NIDDM subjects, 43,8 +/- 2.1 years old. Platelet Cai levels were higher [125.9 +/- 8.1 versus 98.9 +/- 1.4nmol/L] and Ca-ion levels lower [8.9 +/- 0.2 versus 10.3 +/- 0.28mg/dl] in normal elderly compared with young control subjects. Furthermore, platelet Ki and Mgi levels were lower [131 +/- 2.4 versus 146 +/- 3.8mmol/l; 218.4 +/- 9.4micro mol/l versus 326.3 +/- 9.8 micro mol/l] in normal elderly compared with young control subjects. K-ion and Mg-ion levels were also lower [4.4 +/- 0.18 versus 5.4 +/- 0.15mmol/l; 1.86 +/- 0.08 versus 1.92 +/- 0.3mg/dl] in normal elderly compared with young control subjects. These ionic changes mimic those occurring in young hypertensive and young diabetic subjects. We conclude that ageing is associated with alterations of Cai, Ki, Mgi and Ca-ion, K-ion, Mg-ion levels resembling those changes present at any age in hypertension and diabetes. We hypothesize that these alterations of ionic concentrations underlie the predisposition to the alterations of blood pressure and insulin sensitivity characteristic of [normal] ageing